/* 
    rsolve,reject 定义为箭头函数是 为了this的指向指向这个实例化的类 （因为是直接调用，普通函数会指向window/underfied）
*/
const PENDING = 'pending'; //等待
const FULFILLED = 'fulfilled'; //成功
const REJECTED = 'rejected'; //失败

class MyPromise {
    // 接收执行器
    constructor(executor) {
        try {
            executor(this.resolve, this.reject) //执行器立即执行
        }catch(e) {
            this.reject(e)
        }
    }
    // promise 状态
    status = PENDING
    //成功之后的值
    value = undefined;
    //失败后的原因
    reason = undefined;
    // 成功回调
    successCallback = [];
    //失败回调
    failCallback = [];
    resolve = value => {
        //如果状态不是等待 阻止程序向下执行
        if(this.status !== PENDING) return;
        // 将状态更改为成功
        this.status = FULFILLED;
        //保存成功之后的值
        this.value = value

        //判断成功回调是否存在 如果存在就调用
        // this.successCallback &&  this.successCallback(this.value)
        // shift 删除并返回第一个元素
        while(this.successCallback.length) this.successCallback.shift()()
        
    }
    reject = reason => {
        //如果状态不是等待 阻止程序向下执行
        if(this.status !== PENDING) return;
        // 将状态更改为失败
        this.status = REJECTED;
        //保存失败之后的原因
        this.reason = reason;

        //判断失败回调是否存在 如果存在就调用
        // this.failCallback && this.failCallback(this.reason)
        while(this.failCallback.length) this.failCallback.shift()()
    }
    then(successCallback, failCallback) {
        // 如果then没有参数，就手动赋值一个回调函数
        successCallback = successCallback ? successCallback: value => value
        // failCallback = failCallback ? failCallback: reason => reason
        failCallback = failCallback ? failCallback :reason=> {throw reason }
        let promise2 = new Promise((resolve, reject)=> {
            //判断状态
            if(this.status === FULFILLED) {
                setTimeout(() => {
                    try {
                        let x = successCallback(this.value);
                        //判断x是普通值还是promise对象 
                        // 如果是普通值就 直接调用resolve(x)传递给下一个then
                        //如果是promise对象 查看promise对象结果
                        //再根据promise对象的返回结果 决定调用resolve 还是reject
                        resolvePromise(promise2, x, resolve, reject) //判断x的类型
                    }catch(e) {
                        reject(e)
                    }
                }, 0);
            }else if(this.status === REJECTED) {  
                setTimeout(() => {
                    try {
                        let x = failCallback(this.reason);
                        //判断x是普通值还是promise对象 
                        // 如果是普通值就 直接调用resolve(x)传递给下一个then
                        //如果是promise对象 查看promise对象结果
                        //再根据promise对象的返回结果 决定调用resolve 还是reject
                        resolvePromise(promise2, x, resolve, reject) //判断x的类型
                    }catch(e) {
                        reject(e)
                    }
                }, 0);
            }else {
                // 异步进入等待
                // 将成功和失败回调存储起来
                this.successCallback.push(()=> {
                    setTimeout(() => {
                        try {
                            let x = successCallback(this.value);
                            //判断x是普通值还是promise对象 
                            // 如果是普通值就 直接调用resolve(x)传递给下一个then
                            //如果是promise对象 查看promise对象结果
                            //再根据promise对象的返回结果 决定调用resolve 还是reject
                            resolvePromise(promise2, x, resolve, reject) //判断x的类型
                        }catch(e) {
                            reject(e)
                        }
                    }, 0);
                })
                this.failCallback.push(()=> {
                    setTimeout(() => {
                        try {
                            let x = failCallback(this.reason);
                            //判断x是普通值还是promise对象 
                            // 如果是普通值就 直接调用resolve(x)传递给下一个then
                            //如果是promise对象 查看promise对象结果
                            //再根据promise对象的返回结果 决定调用resolve 还是reject
                            resolvePromise(promise2, x, resolve, reject) //判断x的类型
                        }catch(e) {
                            reject(e)
                        }
                    }, 0);
                })
            }
        })
        return promise2;
    }
    finally(callback) {
        return this.then(value=> {
            return MyPromise.resolve(callback()).then(()=>value)
        },reason => {
            return MyPromise.resolve(callback()).then(()=> {throw reason})
        })
    }
    catch(failCallback) {
        return this.then(undefined, failCallback)
    }
    static all (array) {
        let result = [];
        let index = 0;
        return new MyPromise((resolve, reject)=> {
            function addData (key, value) {
                result[key] = value;
                index ++;
                if(index === array.length) {
                    resolve(result);
                }
            }
            for(let i = 0; i<array.length; i++) {
                let current = array[i];
                if(current instanceof MyPromise) {
                    // promise对象
                    current.then(value=> addData(i, value), reason=> reject(reason))
                }else {
                    // 普通值
                    addData(i, array[i])
                }
            }
        })
    }
    static resolve(value) {
        if(value instanceof MyPromise) return value;
        return new MyPromise(resolve => resolve(value))
    }
}
//判断x的类型
function resolvePromise(promise2, x, resolve, reject) {
    if(promise2 === x) {
        return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
    }
    if(x instanceof MyPromise) {
        //promise 对象
        // x.then(value=> resolve(value), reason=> reject(reason))
        x.then(resolve, reject)
    }else {
        //普通值
        resolve(x)
    }
}

module.exports = MyPromise